There are a number of parameters that measure the performance of permanent magnets. The most important of these parameters are coercivity and energy product. Coercivity is the strength of an external field needed to demagnetize the permanent magnet and energy product is a composite of the strength of the magnet and its coercivity.
Until recently, permanent magnets formed of combinations of samarium and cobalt provided the highest parameters of coercivity and energy product. However, cobalt is a strategic material and the main source of cobalt in the United States is southern Africa, particularly Zaire, and political considerations frequently affect the availability and price of cobalt. Additionally, samarium--cobalt magnets are very expensive and their high price has limited their use for many applications.
Because of the foregoing there has been a search for an effective alternative to samarium--cobalt magnets which would provide high coercivity and energy product without the disadvantages of the samarium--cobalt magnets. Recently, such an effective substitute was proposed and this substitute utilizes a ternary compound of iron, boron and a light rare earth, such as neodymium.
Heretofore, magnets have been produced from the iron, boron and rare earth compound by conventional methods of producing magnets in which the ternary compound is melted and cast, the casting is crushed and milled to produce a powder of the desired small particle size, the particles of the powder are field oriented and compacted into the desired size and shape, the compacted powder is sintered at a temperature of at least 1000.degree. C. for a sufficient time period--typically about one hour, and the sintered product is heat treated at about 630.degree. C. for about one hour to enhance and in fact account for a large fraction of the magnetic characteristics of the product. While frequently producing acceptable magnets of the desired parameters, this method has numerous disadvantages and deficiencies.
Foremost among these disadvantages and deficiencies is the necessity that many of the steps of this method be carried out in an inert gas atmosphere, such as argon, because powders of the ternary compound are highly oxidative and cannot be processed in air. Additional disadvantages are non-reproducibility of the product, the complexity of the method, and powder handling problems caused by oxidation. Due to these many disadvantages and deficiencies, the prior method is expensive and results in a relatively high number of unacceptable magnets or rejects being produced.
With the foregoing in mind, it is an object of the present invention to provide a method of producing high performance permanent magnets from iron, boron and a rare earth which obviates the disadvantages and deficiencies of prior methods.
A more specific object of the present invention is to provide an inexpensive method of producing high performance permanent magnets using iron, boron and a rare earth which may be processed in air prior to sintering and which results in the production of a very low number of unacceptable magnets or rejects.